Carbonaceous material for non-aqueous electrolyte secondary battery, negative electrode for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery, and method for producing carbonaceous material for non-aqueous electrolyte secondary battery

ABSTRACT

Provided is a carbonaceous material used in a negative electrode of a non-aqueous electrolyte secondary battery that shows favorable charge/discharge capacities and low resistance and having favorable resistance to oxidative degradation. The carbonaceous material has an average interplanar spacing d002 of the (002) plane of 0.36 to 0.42 nm calculated by using the Bragg equation according to a wide-angle X-ray diffraction method, a specific surface area of 20 to 65 m2/g obtained by a nitrogen adsorption BET three-point method, a nitrogen element content of 0.3 mass % or less, an oxygen element content of 2.5 mass % or less, and an average particle diameter of 1 to 4 μm according to a laser scattering method.

TECHNICAL FIELD

This patent application claims priority under the Paris Convention basedon Japanese Patent Application No. 2015-214335 (filed Oct. 30, 2015) andJapanese Patent Application No. 2015-214338 (filed Oct. 30, 2015), whichis incorporated herein by reference in their entirety.

The present invention relates to a carbonaceous material suitable for anegative electrode of a non-aqueous electrolyte secondary batteryrepresented by a lithium ion secondary battery, a negative electrode fora non-aqueous electrolyte secondary battery, a non-aqueous electrolytesecondary battery, and a method for producing a carbonaceous materialfor a non-aqueous electrolyte secondary battery.

BACKGROUND ART

Lithium ion secondary batteries are widely used for small portabledevices such as mobile phones and notebook computers. For a negativeelectrode material of the lithium ion secondary batteries,non-graphitizable carbon capable of doping (charging) and dedoping(discharging) of lithium in an amount exceeding the theoretical capacityof graphite of 372 mAh/g has been developed (see, e.g., PatentDocument 1) and used.

Non-graphitizable carbon can be obtained by using, for example,petroleum pitch, coal pitch, phenolic resin, or plants as a carbonsource. Among these carbon sources, plants are raw materials that can besustained and stably supplied through cultivation, and are attractingattention because of being inexpensively obtainable. Since acarbonaceous material obtained by calcining a plant-derived carbon rawmaterial has a large number of fine pores, favorable charge/dischargecapacities are expected (e.g., Patent Documents 1 and 2).

On the other hand, due to the growing interest in environmentalproblems, lithium-ion secondary batteries are recently developed foron-board use and are coming into practical use.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Laid-Open Patent Publication No. 9-161801

Patent Document 2: Japanese Laid-Open Patent Publication No. 10-21919

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

Especially, a carbonaceous material used in lithium ion secondarybatteries for on-board use is required to have favorablecharge/discharge capacities as well as resistance to oxidativedegradation and is also required to have low resistance for furtherproviding the output characteristics of the battery.

Therefore, an object of the present invention is to provide acarbonaceous material (carbonaceous material for a non-aqueouselectrolyte secondary battery) used for a negative electrode of anon-aqueous electrolyte secondary battery (e.g., a lithium ion secondarybattery) exhibiting favorable charge/discharge capacities and lowresistance and having favorable resistance to oxidative degradation, anda method for producing the same.

Means for Solving Problem

The present inventors have found that the object can be achieved by acarbonaceous material for a non-aqueous electrolyte secondary battery ofthe present invention described below.

Therefore, the present invention comprises the following preferredaspects.

[1] A carbonaceous material for a non-aqueous electrolyte secondarybattery, having an average interplanar spacing d₀₀₂ of the (002) planewithin a range of 0.36 to 0.42 nm calculated by using the Bragg equationaccording to a wide-angle X-ray diffraction method, a specific surfacearea within a range of 20 to 65 m²/g obtained by a nitrogen adsorptionBET three-point method, a nitrogen element content of 0.3 mass % orless, an oxygen element content of 2.5 mass % or less, and an averageparticle diameter of 1 to 4 μm according to a laser scattering method.

[2] The carbonaceous material for a non-aqueous electrolyte secondarybattery according to [1], wherein the material has a potassium elementcontent of 0.1 mass % or less and an iron element content of 0.02 mass %or less.

[3] The carbonaceous material for a non-aqueous electrolyte secondarybattery according [1] or [2], wherein the material has a true density of1.4 to 1.7 g/cm³ obtained by a butanol method.

[4] A negative electrode for a non-aqueous electrolyte secondarybattery, comprising the carbonaceous material for a non-aqueouselectrolyte secondary battery according to any one of [1] to [3].

[5] A non-aqueous electrolyte secondary battery, comprising the negativeelectrode for a non-aqueous electrolyte secondary battery according to[4].

[6] A method for producing a carbonaceous material for a non-aqueouselectrolyte secondary battery, the method comprising: a calcining stepof calcining a carbon precursor or a mixture of the carbon precursor anda volatile organic substance under an inert gas atmosphere at 800 to1400° C.

[7] The method for producing a carbonaceous material for a non-aqueouselectrolyte secondary battery according to [6], comprising

the calcining step, and

a post-pulverization step and/or a post-classification step of adjustingthe specific surface area of the carbonaceous material obtained by anitrogen adsorption BET three-point method to 20 to 75 m²/g throughpulverization and/or classification.

[8] The method according to [6] or [7], comprising a pre-pulverizationstep and/or a pre-classification step of adjusting the specific surfacearea of the carbon precursor obtained by a nitrogen adsorption BETthree-point method to 100 to 800 m²/g through pulverization and/orclassification.

[9] The method according to any of [6] to [8], wherein the carbonprecursor is derived from a plant.

[10] The method according to any of [6] to [9], wherein the volatileorganic substance is in a solid state at ordinary temperature and has aresidual carbon ratio of less than 5 mass %.

[11] The method according to any of [6] to [10], wherein thecarbonaceous material has an average interplanar spacing d₀₀₂ of the(002) plane within a range of 0.36 to 0.42 nm calculated by using theBragg equation according to a wide-angle X-ray diffraction method, anitrogen element content of 0.3 mass % or less, an oxygen elementcontent of 2.5 mass % or less, and an average particle diameter of 1 to4 μm according to a laser scattering method.

[12] The method according to any of [6] to [11], wherein thecarbonaceous material has a potassium element content of 0.1 mass % orless and an iron element content of 0.02 mass % or less.

[13] The method according to any of [6] to [12], wherein thecarbonaceous material has a true density of 1.4 to 1.7 g/cm³ obtained bya butanol method.

Effect of the Invention

The non-aqueous electrolyte secondary battery using the carbonaceousmaterial for a non-aqueous electrolyte secondary battery or thecarbonaceous material obtained by the production method of the presentinvention has favorable charge/discharge capacities and favorableresistance to oxidative degradation and also has low resistance.

MODES FOR CARRYING OUT THE INVENTION

The following is a description illustrating embodiments of the presentinvention and is not intended to limit the present invention to thefollowing embodiments. In this description, ordinary temperature refersto 25° C.

(Carbonaceous Material for Non-Aqueous Electrolyte Secondary Battery)

A carbonaceous material for a non-aqueous electrolyte secondary batteryof this embodiment is obtained by calcining a carbon precursor or amixture of the carbon precursor and a volatile organic substance underan inert gas atmosphere at 800 to 1400° C., for example. When thecarbonaceous material for a non-aqueous electrolyte secondary battery isobtained in this way, the carbonaceous material can sufficiently becarbonized and can be obtained as a carbonaceous material having finepores suitable for an electrode material.

The carbon precursor is a precursor of a carbonaceous material supplyinga carbon component at the time of production of a carbonaceous materialand can be produced by using a plant-derived carbon material(hereinafter sometimes referred to as “plant-derived char”) as a rawmaterial. Char generally refers to a non-melting/non-softening powderysolid rich in carbon obtained when coal is heated; however, in thisdescription, the char also refers to a non-melting/non-softening powderysolid rich in carbon obtained by heating an organic substance. Thecarbon precursor derived from a plant is advantageous in environmentaland economic aspects from the viewpoint of carbon neutral and easyavailability.

Plants used as raw materials for plant-derived char (hereinaftersometimes referred to as “plant raw materials”) are not particularlylimited. Examples comprise coconut shells, coffee beans, tea leaves,sugarcane, fruits (e.g., mandarin oranges, bananas), straws, shells,broad-leaved trees, needle-leaved trees, and bamboo. These examplescomprise a waste (e.g., used tea leaves) after being used for theoriginal purpose, or a portion of the plant raw material (e.g., bananaor mandarin orange peel). These plants can be used alone or incombination of two or more kinds. Among these plants, coconut shells arepreferable due to easy availability in large amount and industrialadvantages.

The coconut shells are not particularly limited and may be, for example,coconut shells of palm trees (oil palm), coconut trees, Salak, anddouble coconuts. These coconut shells can be used alone or incombination. Coconut shells of coconut trees and palm trees are biomasswaste generated in a large amount after being used for food, detergentraw material, biodiesel oil raw material, etc., and are particularlypreferable.

Although a method of producing a char from a plant raw material is notparticularly limited, for example, the plant raw material can besubjected to a heat treatment (hereinafter sometimes referred to as“pre-calcining”) under an inert gas atmosphere at 300° C. or higher forthe production.

The raw material can also be obtained in the form of char (e.g., coconutshell char).

The carbonaceous material produced from the plant-derived char can bedoped with a large amount of an active material and is thereforebasically suitable for a negative electrode material of a non-aqueouselectrolyte secondary battery. However, the plant-derived char containsa large amount of metal elements contained in the plant. For example,the coconut shell char contains about 0.3 mass % potassium element andabout 0.1 mass % iron element. If such a carbonaceous materialcontaining a large amount of the metallic elements is used as a negativeelectrode, the electrochemical characteristics and safety of thenon-aqueous electrolyte secondary battery may adversely be affected.

The plant-derived char also contains alkali metals other than potassium(e.g., sodium), alkaline earth metals (e.g., magnesium, calcium),transition metals (e.g., iron, copper), and other metals. If thecarbonaceous material contains these metals, impurities are eluted intoan electrolytic solution during dedoping from the negative electrode ofthe non-aqueous electrolyte secondary battery, which may have anunfavorable influence on battery performance and impair safety.

Furthermore, it has been confirmed in studies by the present inventorsthat blockage of fine pores of the carbonaceous material by an ashcontent may occur and adversely affect the charge/discharge capacitiesof the battery.

Therefore, regarding such an ash content (alkali metal, alkaline earthmetal, transition metal, and other elements) contained in theplant-derived char, the ash content is desirably reduced by ademineralization treatment before a calcining step for obtaining thecarbonaceous material. From such a viewpoint, a production method of thepresent invention may comprise a demineralization step of performing thedemineralization treatment of a carbon material, for example, theplant-derived char, to obtain a carbon precursor. The demineralizationmethod is not particular limited and may be implemented by using, forexample, a method of extracting and demineralizing a metal component byusing acidic water containing a mineral acid such as hydrochloric acidand sulfuric acid, an organic acid such as acetic acid and formic acid,etc. (liquid-phase demineralization), or a method of demineralizationthrough exposure to a high-temperature gas phase containing a halogencompound such as hydrogen chloride (gas-phase demineralization).Although not intended to limit the demineralization method to beapplied, description will hereinafter be made of the gas-phasedemineralization, which is preferable since a drying treatment is notrequired after demineralization. The demineralized plant-derived charwill hereinafter also be referred to as a “plant-derived char carbonprecursor”.

For the gas-phase demineralization, it is preferable to perform a heattreatment of the plant-derived char in a gas phase containing a halogencompound. The halogen compound is not particularly limited, and examplesthereof can comprise fluorine, chlorine, bromine, iodine, hydrogenfluoride, hydrogen chloride, hydrogen bromide, iodine bromide, chlorinefluoride (CIF), iodine chloride (ICl), iodine bromide (IBr), and brominechloride (BrCl). Compounds generating these halogen compounds by thermaldecomposition, or a mixture thereof are also usable. From the viewpointsof the stability of the halogen compound to be used and the supplystability thereof, hydrogen chloride is preferable.

For the gas-phase demineralization, the halogen compound and an inertgas may be mixed and used. The inert gas is not particularly limited aslong as the gas is not reactive with the carbon component constitutingthe plant-derived char. For example, the gas can be nitrogen, helium,argon, and krypton, as well as mixtures thereof. From the viewpoints ofsupply stability and economy, nitrogen is preferable.

In the gas-phase demineralization, the mixing ratio of the halogencompound and the inert gas is not limited as long as sufficientdemineralization can be achieved and, for example, from the viewpointsof safety, economy, and persistence in carbon, the amount of the halogencompound relative to the inert gas is preferably 0.01 to 10 vol %, morepreferably 0.05 to 8 vol %, further preferably 0.1 to 5 vol %.

The temperature of the gas-phase demineralization may be varieddepending on the plant-derived char that is the object of thedemineralization and, from the viewpoint of obtaining desired nitrogenelement content and oxygen element content, for example, thedemineralization can be performed at 500 to 950° C., preferably 600 to940° C., more preferably 650 to 940° C., further preferably 850 to 930°C. If the demineralization temperature is too low, demineralizationefficiency may decrease so that the demineralization may notsufficiently be performed. If the demineralization temperature is toohigh, activation by the halogen compound may occur.

The time of the gas-phase demineralization is not particularly limitedand is, for example, 5 to 300 minutes, preferably 10 to 200 minutes,more preferably 20 to 150 minutes, from the viewpoints of economicefficiency of reaction equipment and structural retention of the carboncontent.

In the gas-phase demineralization in this embodiment, potassium, iron,etc. contained in the plant-derived char are removed. The potassiumelement content contained in the carbon precursor obtained after thegas-phase demineralization is preferably 0.1 mass % or less, morepreferably 0.05 mass % or less, further preferably 0.03 mass % or less,from the viewpoints of increasing a dedoping capacity and decreasing anon-dedoping capacity. The iron element content contained in the carbonprecursor obtained after the gas-phase demineralization is preferably0.02 mass % or less, more preferably 0.015 mass % or less, furtherpreferably 0.01 mass % or less from the viewpoints of increasing thededoping capacity and decreasing the non-dedoping capacity. When thecontents of the potassium element and the iron element contained in thecarbon precursor become larger, the dedoping capacity may be decreasedin the non-aqueous electrolyte secondary battery using the obtainedcarbonaceous material. Additionally, the non-dedoping capacity may beincreased. Furthermore, when these metal elements are eluted into theelectrolytic solution and reprecipitated, a short circuit may occur andmay cause a significant problem in safety of the non-aqueous electrolytesecondary battery. It is particularly preferable that the plant-derivedchar carbon precursor after the gas-phase demineralization does notsubstantially contain the potassium element and the iron element.Details of measurement of the contents of the potassium element and theiron element are as described in Examples, and a fluorescent X-rayanalyzer (e.g., “LAB CENTER XRF-1700” manufactured by ShimadzuCorporation) can be used. The potassium element content and the ironelement content contained in the carbon precursor are normally 0 mass %or more.

The particle diameter of the plant-derived char to be subjected to thegas-phase demineralization is not particularly limited; however, anexcessively small particle diameter may make it difficult to separatethe gas phase containing removed potassium etc. and the plant-derivedchar, and therefore, a lower limit of the average value (D50) of theparticle diameter is preferably 100 μm or more, more preferably 300 μmor more, further preferably 500 μm or more. An upper limit of theaverage value of the particle diameter is preferably 10000 μm or less,more preferably 8000 μm or less, further preferably 5000 μm or less fromthe viewpoint of fluidity in a mixed gas stream. Details of measurementof the particle diameter are as described in Examples and, for example,a laser scattering method can be performed by using a particle sizedistribution measuring device (e.g., “SALD-3000S” manufactured byShimadzu Corporation, “Microtrac MT3000” manufactured by Nikkiso).

An apparatus used for the gas-phase demineralization is not particularlylimited as long as the apparatus is capable of heating while mixing theplant-derived char and the gas phase containing a halogen compound. Forexample, a fluidized furnace can be used for using an intra-layer flowsystem of a continuous type with a fluidized bed etc. or a batch type.Although a supply amount (flow rate) of the gas phase is notparticularly limited, from the viewpoint of fluidity in a mixed gasstream, for example, the gas phase is supplied at preferably 1 ml/min ormore, more preferably 5 ml/min or more, and further preferably 10 ml/minor more per 1 g of the plant-derived char.

In the gas-phase demineralization, after the heat treatment in an inertgas atmosphere containing a halogen compound (hereinafter sometimesreferred to as a “halogen heat treatment”), preferably, a heat treatmentin the absence of a halogen compound (hereinafter sometimes referred toas a “gas-phase deacidification treatment”) is further performed. Sincehalogen is contained in the plant-derived char due to the halogen heattreatment, the halogen contained in the plant-derived char is preferablyremoved by the gas-phase deacidification treatment. Specifically, thegas-phase deacidification treatment is performed in an inert gasatmosphere containing no halogen compound at, for example, 500° C. to940° C., preferably 600° C. to 940° C., more preferably 650° C. to 940°C., further preferably 850° C. to 930° C., and the temperature of theheat treatment is preferably the same as or higher than the temperatureof the first heat treatment. For example, halogen can be removed byperforming a heat treatment with the supply of the halogen compoundbeing blocked after the halogen heat treatment. The time of thegas-phase deoxidation treatment is also not particularly limited and ispreferably 5 to 300 minutes, more preferably 10 to 200 minutes, furtherpreferably 10 to 100 minutes.

The carbon precursor can be adjusted in average particle diameterthrough a pulverization step and/or a classification step as needed. Thepulverization step and/or the classification step is preferablyperformed after the demineralization treatment. In the followingdescription, the pulverization step and the classification stepperformed before the calcining step are also referred to as apre-pulverization step and a pre-classification step, respectively. Thepulverization step and the classification step performed after thecalcining step are also referred to as a post-pulverization step and apost-classification step. In the production method of the presentinvention, it is preferable to perform the pre-pulverization step andthe pre-classification step after the demineralization treatment.

In a preferable embodiment of the production method of the presentinvention, at the pulverization step and/or the classification step (thepre-pulverization step and the pre-classification step), the carbonprecursor is preferably pulverized and/or classified before thecalcining step such that the average particle diameter of thecarbonaceous material after the calcining step falls within a range of,for example, 1 to 4 μm, from the viewpoint of coatability duringelectrode fabrication. Therefore, the average particle diameter (D50) ofthe carbonaceous material of this embodiment is adjusted to the range of1 to 4 μm, for example. Only the pulverization step or theclassification step may be performed, or both the pulverization step andthe classification step may be performed.

The pulverization step and/or the classification step (thepost-pulverization step and/or the post-classification step) can beperformed after the calcining step of the carbon precursor to adjust theaverage particle diameter of the carbonaceous material within the range.

In another preferred embodiment of the production method of the presentinvention in which the post-pulverization step and/or thepost-classification step are performed, at the pre-pulverization stepand/or the pre-classification step before the calcining step, the carbonprecursor is preferably pulverized and/or classified such that theaverage particle diameter (D50) of the carbon precursor falls within arange of 5 to 800 μm from the viewpoint of uniformity duringcalcination. Therefore, the average particle diameter (D50) of thecarbon precursor of this embodiment is adjusted to the range of 5 to 800μm, for example. As long as the carbon precursor having an averageparticle diameter within the range can be obtained, only thepre-pulverization step or the pre-classification step may be performed,or both the pre-pulverization step and the pre-classification step maybe performed. When the average particle diameter is 5 μm or more, finepowder hardly scatters in a calcining furnace during calcination,thereby resulting in an excellent recovery rate of the generatedcarbonaceous material as well as a suppression of an apparatus load. Onthe other hand, when the average particle diameter is 800 μm or less,the process of gas emitted from the particles during calcination ishardly elongated, resulting in favorable uniformity on the inside andthe outside of the carbonaceous material. From such a viewpoint, theaverage particle diameter is preferably 800 μm or less, more preferably700 μm or less, further preferably 600 μm or less, particularlypreferably 500 μm or less, most preferably 400 μm or less.

In the preferred embodiment described above, by performing thepre-pulverization step and/or the pre-classification step and furtherperforming the post-pulverization step and/or the post-classificationstep, the particles adjusted in particle size by the pre-pulverizationare supplied so that a post-pulverization property is stabilized, whichnot only facilitates adjustment of particles having a desired particlesize distribution but also provides an improvement in recovery rate dueto stabilization of the particle size distribution. Furthermore, thepost-classification makes it easier to perform the calcination such thatthe desired particle size distribution is achieved.

Therefore, in the present invention, the pulverization step and/or theclassification step may be performed before the calcining step, afterthe calcining step, or both before and after the calcining step.

When the average particle diameter of the carbonaceous material is lessthan 1 μm, since an increase in fine powder increases the specificsurface area, a higher reactivity with an electrolytic solutionincreases an irreversible capacity that is a capacity not to bedischarged even when charged, and therefore, the capacity of thepositive electrode may be wasted in an increased proportion.Additionally, when a negative electrode is produced by using theobtained carbonaceous material, smaller gaps are formed in thecarbonaceous material, so that migration of lithium ions in theelectrolytic solution may be suppressed. The average particle diameter(D50) of the carbonaceous material of the present invention ispreferably 1 μm or more, more preferably 1.5 μm or more, furtherpreferably 1.7 μm or more. On the other hand, the average particlediameter of 4 μm or less is preferable since a small diffusion free pathof lithium ions in the particles enables rapid charging and discharging.Furthermore, in lithium ion secondary batteries, it is important toincrease an electrode area for improvement of input/outputcharacteristics, and therefore, a coating thickness of an activematerial applied to a collector plate needs to be reduced at the time ofelectrode fabrication. To reduce the coating thickness, it is necessaryto reduce the particle diameter of the active material. From such aviewpoint, the average particle diameter is preferably 4 μm or less,more preferably 3.5 μm or less, further preferably 3.2 μm or less,particularly preferably 3 μm or less, most preferably 2.8 μm or less.

The plant-derived char carbon precursor shrinks by about 0 to 20%depending on conditions of main calcination described later. Therefore,when the pulverization step and/or the classification step is performedonly before the calcining step, the average particle diameter of theplant-derived char carbon precursor is preferably adjusted to a particlediameter larger by about 0 to 20% than a desired post-calcining averageparticle diameter so as to achieve the post-calcining average particlediameter of 1 to 4 μm. Therefore, when the pulverization step and/or theclassification step is performed only before the calcining step,pulverization and/or classification is preferably performed such thatthe average particle diameter after pulverization and/or classificationis preferably 1 to 5 μm, more preferably 1.1 to 4.4 μm.

Since the carbon precursor does not melt even when a heat treatment stepdescribed later is performed, the pulverization step is not particularlylimited in terms of order as long as the pulverization step is performedafter the demineralization step. From the viewpoint of reduction inspecific surface area of the carbonaceous material, the pulverizationstep is preferably performed before the calcining step. This is becauseif the plant-derived char is mixed with a volatile organic substance asnecessary and calcined before pulverization, the specific surface areamay not sufficiently be reduced. However, it is not intended to excludeperforming the pulverization step after the calcining step.

A pulverizing apparatus used for the pulverization step is notparticularly limited and, for example, a jet mill, a ball mill, a beadmill, a hammer mill, or a rod mill can be used. In terms of theefficiency of pulverization, a system performing pulverization throughcontact between particles such as a jet mill has a longer pulverizationtime and a lower volume efficiency, so that a system performingpulverization in the presence of a pulverization media such as a ballmill and a bead mill is preferable, and the use of a bead mill ispreferable from the viewpoint of avoiding impurities mixed in from thepulverization media, while the use of a ball mill is preferable from theviewpoint of equipment load.

In one embodiment of the present invention, the classification step canbe performed after the pulverization step. By the classification stepafter the pulverization step, the average particle diameter of thecarbonaceous material can more accurately be adjusted. For example,particles having a particle diameter of 1 μm or less can be removed, andcoarse particles having a particle diameter of 800 μm or more can beremoved.

Although not particularly limited, examples of a classification methodcan comprise classification using a sieve, wet classification, and dryclassification. Examples of wet classifiers can comprise classifiersutilizing principles of gravity classification, inertia classification,hydraulic classification, and centrifugal classification. Examples ofdry classifiers can comprise classifiers utilizing principles ofsedimentation classification, mechanical classification, centrifugalclassification, etc.

In this embodiment, the specific surface area of the carbon precursorafter pulverization and/or classification (the pre-pulverization stepand/or the pre-classification step) is preferably 100 to 800 m²/g, morepreferably 200 to 700 m²/g, for example, 200 to 600 m²/g. Thepulverization step and/or the classification step is preferablyperformed such that the carbon precursor having a specific surface areawithin the range is obtained. As long as the carbon precursor having aspecific surface area within the range can be obtained, only thepulverization step or the classification step may be performed, or boththe pulverization step and the classification step may be performed. Ifthe specific surface area is too small, the fine pores of thecarbonaceous material may not sufficiently be reduced even after thecalcining step described later, and the hygroscopicity of thecarbonaceous material may hardly be reduced. If moisture is present inthe carbonaceous material, problems may be caused by generation of anacid accompanying hydrolysis of the electrolytic solution and generationof a gas due to electrolysis of water. Additionally, the oxidation ofthe carbonaceous material may progress under the air atmosphere and maycause a significant change in battery performance. If the specificsurface area becomes too large, the specific surface area of thecarbonaceous material does not become small even after the calciningstep described later, and the utilization efficiency of lithium ions maydecrease in the non-aqueous electrolyte secondary battery. The specificsurface area of the carbon precursor can also be adjusted by controllingthe temperature of the gas-phase demineralization. In this description,the specific surface area means a specific surface area (BET specificsurface area) determined by a BET method (nitrogen adsorption BETthree-point method). Specifically, the specific surface area can bemeasured by using a method described later.

In one embodiment of the present invention, the method for producing acarbonaceous material for a non-aqueous electrolyte secondary battery ofthe present embodiment comprises a step of calcining a carbon precursoror a mixture of the carbon precursor and a volatile organic substanceunder an inert gas atmosphere at 800 to 1400° C. to obtain thecarbonaceous material (hereinafter sometimes referred to as a “calciningstep”). By comprising the calcining step, the non-aqueous electrolytesecondary battery using the obtained carbonaceous material has favorabledischarge capacity and favorable resistance to oxidative deterioration.The calcining step is preferably performed after the demineralizationstep and preferably performed after the demineralization step, thepre-pulverization step, and the pre-classification step.

By calcining a carbon precursor or a mixture of the carbon precursor anda volatile organic substance, the carbonaceous material of the presentembodiment is obtained. By mixing and calcining the carbon precursor andthe volatile organic substance, the specific surface area of theobtained carbonaceous material can be reduced to achieve the specificsurface area suitable for the negative electrode material for thenon-aqueous electrolyte secondary battery. Furthermore, an adsorptionamount of carbon dioxide to the carbonaceous material can be adjusted.

Although details are not clarified in terms of the mechanism in whichthe specific surface area of the carbonaceous material is reduced bymixing and calcining the carbon precursor and the volatile organicsubstance, this can be thought as follows. However, the presentinvention is not limited by the following description. It is thoughtthat a carbonaceous coating film obtained by a heat treatment of avolatile organic substance is formed on the surface of the plant-derivedchar carbon precursor by mixing and calcining the plant-derived charcarbon precursor and the volatile organic substance. The carbonaceouscoating film reduces the specific surface area of the carbonaceousmaterial generated from the plant-derived char carbon precursor andsuppresses a formation reaction of a coating film called SEI (SolidElectrolyte Interphase) due to a reaction between the carbonaceousmaterial and lithium, and therefore, it can be expected that theirreversible capacity is reduced. Additionally, since the generatedcarbonaceous coating film can be doped and dedoped with lithium, aneffect of increasing the capacity can also be expected.

Although not particularly limited, examples of the volatile organicsubstance comprise thermoplastic resins and low-molecular organiccompounds. Specifically, examples of the thermoplastic resins cancomprise polystyrene, polyethylene, polypropylene, poly(meth)acrylicacid, poly(meth)acrylic acid ester, etc. In this description,(meth)acryl is a generic term for acryl and methacryl. Examples of thelow-molecular organic compounds can comprise toluene, xylene,mesitylene, styrene, naphthalene, phenanthrene, anthracene, pyrene, etc.Since it is preferable that the substance volatilizes under thecalcining temperature and does not oxidize or activate the surface ofthe carbon precursor when thermally decomposed, the thermoplastic resinis preferably polystyrene, polyethylene, or polypropylene. From theviewpoint of safety, it is preferable that the low-molecular organiccompound has low volatility under ordinary temperature and, therefore,naphthalene, phenanthrene, anthracene, pyrene etc. are preferable.

In one embodiment of the present invention, examples of thethermoplastic resins can comprise an olefin-based resin, a styrene-basedresin, and a (meth)acrylic acid-based resin. Examples of theolefin-based resin can comprise polyethylene, polypropylene, randomcopolymers of ethylene and propylene, block copolymers of ethylene andpropylene, etc. Examples of the styrene-based resin can comprisepolystyrene, poly(α-methylstyrene), copolymers of styrene and(meth)acrylic acid alkyl ester (with an alkyl group having the carbonnumber of 1 to 12, preferably 1 to 6), etc. Examples of the(meth)acrylic acid-based resin can comprise polyacrylic acid,polymethacrylic acid, and (meth)acrylic acid alkyl ester polymers (withan alkyl group having the carbon number of 1 to 12, preferably 1 to 6),etc.

In one embodiment of the present invention, for example, a hydrocarboncompound having the carbon number of 1 to 20 can be used as thelow-molecular organic compound. The carbon number of the hydrocarboncompound is preferably 2 to 18, more preferably 3 to 16. The hydrocarboncompound may be a saturated hydrocarbon compound or an unsaturatedhydrocarbon compound and may be a chain hydrocarbon compound or a cyclichydrocarbon compound. In the case of the unsaturated hydrocarboncompound, the unsaturated bond may be a double bond or a triple bond,and the number of unsaturated bonds contained in one molecule is notparticularly limited. For example, the chain hydrocarbon compound is analiphatic hydrocarbon compound and can be a linear or branched alkane,alkene, or alkyne. The cyclic hydrocarbon compound can be an alicyclichydrocarbon compound (e.g., cycloalkane, cycloalkene, cycloalkyne) or anaromatic hydrocarbon compound. Specifically, the aliphatic hydrocarboncompound can be methane, ethane, propane, butane, pentane, hexane,octane, nonane, decane, ethylene, propylene, butene, pentene, hexene,acetylene, etc. The alicyclic hydrocarbon compound can be cyclopentane,cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclopropane,cyclopentene, cyclohexene, cycloheptene, cyclooctene, decalin,norbornene, methylcyclohexane, and norbornadiene. The aromatichydrocarbon compound can be a monocyclic aromatic compound such asbenzene, toluene, xylene, mesitylene, cumene, butylbenzene, styrene,α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene,vinylxylene, p-tert-butylstyrene, and ethylstyrene, and a condensedpolycyclic aromatic compound with three to six rings such asnaphthalene, phenanthrene, anthracene, and pyrene, and is preferably thecondensed polycyclic aromatic compounds, more preferably naphthalene,phenanthrene, anthracene or pyrene. The hydrocarbon compound may have anarbitrary substituent. Although not particularly limited, thesubstituent can be, for example, an alkyl group having the carbon numberof 1 to 4 (preferably an alkyl group having the carbon number of 1 to2), an alkenyl group having the carbon number of 2 to 4 (preferably analkenyl having the carbon number of 2), and a cycloalkyl group havingthe carbon number of 3 to 8 (preferably a cycloalkyl group having thecarbon number of 3 to 6).

From the viewpoint of ease of mixing and avoidance of unevendistribution (uniform dispersion), the volatile organic substance ispreferably in a solid state at ordinary temperature and is morepreferably a thermoplastic resin that is solid at ordinary temperaturesuch as polystyrene, polyethylene, or polypropylene, or a low-molecularorganic compound that is solid at ordinary temperature such asnaphthalene, phenanthrene, anthracene, or pyrene, for example. Since itis preferable that the substance does not oxidize or activate thesurface of the plant-derived char carbon precursor when volatilized andthermally decomposed under the calcining temperature, the thermoplasticresin is preferably an olefin-based resin and a styrene-based resin,more preferably polystyrene, polystyrene, and polypropylene. Thelow-molecular organic compound is further preferably less volatile underordinary temperature for safety and is therefore preferably ahydrocarbon compound having the carbon number of 1 to 20, morepreferably a condensed polycyclic aromatic compound, further preferablynaphthalene, phenanthrene, anthracene, or pyrene. Moreover, from theviewpoint of ease of mixing with the carbon precursor, the volatileorganic substance is preferably the thermoplastic resin, more preferablythe olefin-based resin and the styrene-based resin, further preferablypolystyrene, polyethylene, and polypropylene, particularly preferablypolystyrene and polyethylene.

From the viewpoint of stable operation of a calcining apparatus, thevolatile organic substance is an organic substance having a residualcarbon ratio of preferably less than 5 mass %, more preferably less than3 mass %. The residual carbon ratio in the present invention ispreferably a residual carbon ratio in the case of ashing at 800° C. Thevolatile organic substance is preferably a substance generating avolatile substance (e.g., a hydrocarbon-based gas or a tar component)capable of reducing the specific surface area of the carbon precursorproduced from the plant-derived char. From the viewpoint of maintainingthe properties of the carbonaceous material generated after calcination,the residual carbon ratio is preferably less than 5 mass %. When theresidual carbon ratio is less than 5%, carbonaceous materials differentin local properties are hardly generated.

The residual carbon ratio can be measured by quantifying a carboncontent of an ignition residue after ignition of a sample in an inertgas. With regard to the ignition, about 1 g of a volatile organicsubstance (the accurate mass is defined as W₁ (g)) is put into acrucible and the crucible is heated in an electric furnace at thetemperature increase rate of 10° C./min from ordinary temperature to800° C. while flowing 20 liters of nitrogen per minute and is thenignited at 800° C. for 1 hour. A residue in this case is regarded as theignition residue, and the mass thereof is defined as W₂ (g).

Subsequently, for the ignition residue, elemental analysis is performedin accordance with the method defined in JIS M 8819 to measure a massproportion P₁ (%) of carbon. A residual carbon ratio P₂ (mass %) can becalculated by following Eq. I.

$\begin{matrix}\left\lbrack {{Mathematical}\mspace{14mu} 1} \right\rbrack & \; \\{P_{2} = {P_{1} \times \frac{W_{2}}{W_{1}}}} & (I)\end{matrix}$

In the case of mixing the carbon precursor and the volatile organicsubstance, although the mass ratio of the carbon precursor and thevolatile organic substance in the mixture is not particularly limited,the mass ratio of the carbon precursor and the volatile organicsubstance is preferably 97:3 to 40:60. The mass ratio of the carbonprecursor and the volatile organic substance in the mixture is morepreferably 95:5 to 60:40, further preferably 93:7 to 80:20. For example,when the mass ratio of the carbon precursor and the volatile organicsubstance is within the range, adjustment to a desired specific surfacearea is facilitated. For example, when the volatile organic substance is3 parts by mass or more, the specific surface area can sufficiently bereduced. When the amount of the volatile organic substance is 60 partsby mass or less, the effect of reducing the specific surface area is notsaturated and the volatile organic substance is hardly excessivelyconsumed, which is industrially advantageous.

Mixing of the carbon precursor and the volatile organic substance liquidor solid at ordinary temperature may be performed either before thepre-pulverization step or after the pre-pulverization step.

In the case of mixing the carbon precursor and the volatile organicsubstance before the pre-pulverization step, pulverization and mixingcan be performed at the same time by weighing and supplying the carbonprecursor and the volatile organic substance that is liquid or solid atordinary temperature simultaneously to the pulverizing apparatus. In thecase of using the volatile organic substance that is gaseous at ordinarytemperature, a method of mixing with the plant-derived char carbonprecursor can comprise allowing a non-oxidizing gas containing thegaseous volatile organic substance to flow into a heat treatmentapparatus containing the plant-derived char carbon precursor for thermaldecomposition.

In the case of mixing after the pre-pulverization step, a mixing methodcan be implemented by using any known mixing method that is a techniquein which both are uniformly mixed. Although the volatile organicsubstance solid at ordinally temperature is preferably mixed in a formof particles, the particle shape and the particle diameter are notparticularly limited. From the viewpoint of uniformly dispersing thevolatile organic substance in the pulverized carbon precursor, theaverage particle diameter of the volatile organic substance ispreferably 0.1 to 2000 μm, more preferably 1 to 1000 μm, furtherpreferably 2 to 600 μm.

The carbon precursor or mixture described above may contain a componentother than the carbon precursor and the volatile organic substance. Forexample, the mixture can contain natural graphite, artificial graphite,a metal-based material, an alloy-based material, or an oxide-basedmaterial. The content of the other component is not particularly limitedand is preferably 50 parts by mass or less, more preferably 30 parts bymass or less, further preferably 20 parts by mass or less, mostpreferably 10 parts by mass or less based on 100 parts by mass of thecarbon precursor or the mixture of the carbon precursor and the volatileorganic substance.

At the calcining step in the production method of the presentembodiment, the carbon precursor or the mixture of the carbon precursorand the volatile organic substance is preferably calcined at 800 to1400° C. The present invention also provides a method for producing acarbonaceous material for a non-aqueous electrolyte secondary battery,comprising a calcining step of calcining a carbon precursor or a mixtureof the carbon precursor and a volatile organic substance under an inertgas atmosphere at 800 to 1400° C. to obtain the carbonaceous material.

The calcining step may comprise

(a) a calcining step of calcining the pulverized carbon precursor ormixture at 800 to 1400° C. for main calcination, or may comprise

(b) a calcining step of preliminarily calcining the pulverized carbonprecursor or mixture at 350° C. or higher and less than 800° C. andsubsequently performing main calcination at 800 to 1400° C.

If the calcining step (a) is performed, it is thought that coating ofthe carbon precursor with the tar component and the hydrocarbon-basedgas occurs at the step of main calcination. If the calcining step (b) isperformed, it is thought that coating of the carbon precursor with thetar component and the hydrocarbon-based gas occurs at the step ofpreliminary calcination.

An example of procedures of the preliminary calcination and the maincalcination will hereinafter be described as an embodiment of thepresent invention; however, the present invention is not limitedthereto.

(Preliminary Calcination)

The preliminary calcining step in this embodiment can be performed, forexample, by calcining the pulverized carbon precursor or mixture at 350°C. or higher and less than 800° C. Volatile matters (such as CO₂, CO,CH₄, and H₂) and the tar component can be removed by the preliminarycalcining step. The generation of the volatile matters and the tarcomponent at the main calcining step performed after the preliminarycalcining step can be reduced, and a burden on a calcining machine canbe reduced.

The preliminary calcining step is preferably performed at 350° C. orhigher, more preferably at 400° C. or higher. The preliminary calciningstep can be performed according to a usual preliminary calciningprocedure. Specifically, the preliminary calcination can be performed inan inert gas atmosphere. Examples of the inert gas can comprisenitrogen, argon, etc. The preliminary calcination may be performed underreduced pressure and can be performed at 10 kPa or less, for example.The preliminary calcination is not particularly limited in terms of timeand can be performed, for example, within the range of 0.5 to 10 hours,more preferably 1 to 5 hours.

(Main Calcination)

The main calcining step can be performed according to a usual maincalcining procedure. By performing the main calcination, a carbonaceousmaterial for a non-aqueous electrolyte secondary battery can beobtained.

A specific temperature of the main calcining step is preferably 800 to1400° C., more preferably 1000 to 1350° C., further preferably 1100 to1300° C. The main calcination is performed under an inert gasatmosphere. Examples of the inert gas can comprise nitrogen, argon,etc., and the main calcination can be performed in an inert gascontaining a halogen gas. The main calcining step can be performed underreduced pressure and can be performed at 10 kPa or less, for example.The main calcining step is not particularly limited in terms ofexecution time and can be performed, for example, for 0.05 to 10 hours,preferably 0.05 to 8 hours, more preferably 0.05 to 6 hours.

As described above, a calcined material (carbonaceous material) may beadjusted to the predetermined average particle diameter by performingthe pulverization step and/or the classification step (thepost-pulverization step and/or the post-classification step) after thecalcining step. In the present invention, performing the pulverizationstep and/or the classification step after the calcining step has anadvantage in terms of process control such as absence of scattering offine powder during firing.

Therefore, the production method of the present invention preferablycomprises the calcining step, and the post-pulverization step and/or thepost-classification step of adjusting the specific surface area of thecalcined material (carbonaceous material) obtained at the calcining stepto 20 to 75 m²/g through pulverization and/or classification. After thecalcining step, the calcined material (carbonaceous material) can havethe average particle diameter adjusted by the post-pulverization stepand/or post-classification step. In the present invention, performingthe post-pulverization step and/or the post-classification step afterthe calcining step is preferable from the viewpoint of process controlbecause of absence of scattering of fine powder during firing etc., andwhen the obtained carbonaceous material is used for a non-aqueouselectrolyte secondary battery, the production method of the presentinvention comprising the post-pulverization step and/or thepost-classification step after the calcining step improves the effectivesurface area of the obtained carbonaceous material brought into contactwith the electrolytic solution so that low resistance can be achieved.

The specific surface area of the carbonaceous material of the presentinvention is 20 m²/g to 65 m²/g, preferably 22 m²/g to 65 m²/g, morepreferably 25 m²/g to 60 m²/g, further preferably 25 m²/g to 55 m²/g,for example 26 m²/g to 50 m²/g. When the specific surface area is toosmall, an adsorption amount of lithium ions to the carbonaceous materialdecreases, and the charge capacity of the non-aqueous electrolytesecondary battery may be reduced. When the specific surface area is toohigh, lithium ions react on the surface of the carbonaceous material andare consumed, so that the utilization efficiency of lithium ions becomeslower.

In a preferable embodiment of the production method of the presentinvention, the specific surface area of the carbonaceous materialobtained by the production method of the present invention is preferably20 m²/g to 75 m²/g, more preferably 22 m²/g to 73 m²/g, furtherpreferably 24 m²/g to 71 m²/g, further preferably 26 m²/g to 70 m²/g,particularly preferably from 26 m²/g to 60 m²/g, most preferably from 26m²/g to 50 m²/g. In the production method of the present invention, thepost-pulverization step and/or the post-classification step ispreferably performed such that the carbon precursor having a specificsurface area within the range is obtained. When the specific surfacearea is too small, an adsorption amount of lithium ions to thecarbonaceous material decreases, and the charge capacity of thenon-aqueous electrolyte secondary battery may be reduced. When thespecific surface area is too high, lithium ions react on the surface ofthe carbonaceous material and are consumed, so that the utilizationefficiency of lithium ions may become lower.

Other method of adjusting the specific surface area to the range are notlimited at all and, for example, a method of adjusting the calciningtemperature and calcining time of the carbon precursor resulting in thecarbonaceous material can be used. Specifically, since the specificsurface area tends to decrease when the calcining temperature is madehigher or the calcining time is made longer, the calcining temperatureand the calcining time may be adjusted to obtain the specific surfacearea within the range. A method of mixing and calcining with a volatileorganic substance may be used. As described above, it is thought that acarbonaceous coating film obtained by a heat treatment of a volatileorganic substance is formed on the surface of the carbon precursor bymixing and calcining the carbon precursor and the volatile organicsubstance. It is thought that the carbonaceous coating film reduces thespecific surface area of the carbonaceous material obtained from thecarbon precursor. Therefore, by adjusting the amount of the volatileorganic substance to be mixed, the specific surface area of thecarbonaceous material can be adjusted to the range.

In a preferable form of the production method of the present invention,the average particle diameter (D50) of the carbonaceous materialobtained by the production method of the present invention is preferablyin the range of 1 to 4 μm from the viewpoint of coatability duringelectrode fabrication. Therefore, the average particle diameter (D50) ofthe carbonaceous material of this embodiment is adjusted to the range of1 to 4 μm, for example. As long as the carbonaceous material having anaverage particle diameter within the range can be obtained, only thepost-pulverization step or the post-classification step may beperformed, or both the post-pulverization step and thepost-classification step may be performed. When the average particlediameter is less than 1 μm, since increased fine powder increases thespecific surface area, a higher reactivity with an electrolytic solutionincreases an irreversible capacity that is a capacity not to bedischarged even when charged, and therefore, the capacity of thepositive electrode may be wasted in an increased proportion.Additionally, when a negative electrode is produced by using theobtained carbonaceous material, smaller gaps are formed in thecarbonaceous material, so that migration of lithium ions in theelectrolytic solution may be suppressed. The average particle diameter(D50) of the carbonaceous material obtained from the present inventionis preferably 1 μm or more, more preferably 1.5 μm or more, furtherpreferably 1.7 μm or more. On the other hand, when the average particlediameter is 4 μm or less, a small diffusion free path of lithium ions inthe particles enables rapid charging and discharging. Furthermore, inlithium ion secondary batteries, it is important to increase anelectrode area for improvement of input/output characteristics, andtherefore, a coating thickness of an active material applied to acollector plate needs to be reduced at the time of electrodefabrication. To reduce the coating thickness, it is necessary to reducethe particle diameter of the active material. From such a viewpoint, theaverage particle diameter is preferably 4 μm or less, more preferably3.5 μm or less, further preferably 3.2 μm or less, particularlypreferably 3.1 μm or less, most preferably 2.9 μm or less.

A pulverizing apparatus used for the post-pulverization step is notparticularly limited and, for example, a jet mill, a ball mill, a beadmill, a hammer mill, or a rod mill can be used. In terms of theefficiency of pulverization, a system performing pulverization throughcontact between particles such as a jet mill has a longer pulverizationtime and a lower volume efficiency, so that a system performingpulverization in the presence of a pulverization media such as a ballmill and a bead mill is preferable, and the use of a bead mill ispreferable from the viewpoint of avoiding impurities mixed in from thepulverization media.

By the post-classification step, the average particle diameter of thecarbonaceous material can more accurately be adjusted. For example,particles having a particle diameter of 0.5 μm or less can be removed,and coarse particles can be removed.

Although not particularly limited, examples of a classification methodcan comprise classification using a sieve, wet classification, and dryclassification. Examples of wet classifiers can comprise classifiersutilizing principles of gravity classification, inertia classification,hydraulic classification, and centrifugal classification. Examples ofdry classifiers can comprise classifiers utilizing principles ofsedimentation classification, mechanical classification, centrifugalclassification, etc.

In the carbonaceous material of the present invention, an averageinterplanar spacing d₀₀₂ of the (002) plane calculated by using theBragg equation according to a wide-angle X-ray diffraction method is0.36 nm to 0.42 nm, preferably 0.38 nm to 0.4 nm, more preferably 0.382nm to 0.396 nm. When the average interplanar spacing d₀₀₂ of the (002)plane is too small, the resistance may become large when lithium ionsare inserted into the carbonaceous material, and the resistance at thetime of output may become large, so that input/output characteristicsfor a lithium ion secondary battery may deteriorate. Moreover, since thecarbonaceous material repeatedly expands and shrinks, stability for theelectrode material may be impaired. When the average interplanar spacingd₀₀₂ is too large, the volume of the carbonaceous material becomes largealthough the diffusion resistance of lithium ions becomes small, so thatan effective capacity per volume may be reduced. The carbonaceousmaterial obtained by the production method of the present invention alsopreferably has the average interplanar spacing d₀₀₂ of in the range.

A method of adjusting the average interplanar spacing to the range isnot limited at all and, for example, the calcining temperature of thecarbon precursor resulting in the carbonaceous material may be set inthe range of 800 to 1400° C. A method of mixing and calcining with athermally decomposable resin such as polystyrene can also be used.

A nitrogen element content contained in the carbonaceous material of thepresent invention is preferably as small as possible and usually has ananalysis value obtained from elemental analysis of preferably 0.3 mass %or less, more preferably 0.28 mass % or less, further preferably 0.25mass % or less, further preferably 0.2 mass % or less, particularlypreferably 0.18 mass % or less. It is further preferable that thenitrogen element is not substantially contained in the carbonaceousmaterial. As used herein, “not substantially contained” means that thecontent is equal to or less than 10⁻⁶ mass %, which is a detection limitof an elemental analysis method (inert gas fusion-thermal conductimetry)described later. If the nitrogen element content is too large, lithiumions and nitrogen react with each other and lithium ions are consumed,thereby not only reducing the utilization efficiency of lithium ions butalso causing a reaction with oxygen in air during storage in some cases.The carbonaceous material obtained by the production method of thepresent invention also preferably has the nitrogen element content inthe range.

A method of adjusting the nitrogen element content to the range is notlimited at all and, for example, the plant-derived char can be subjectedto gas-phase demineralization by a method comprising a step of heattreatment at 500° C. to 940° C. in an inert gas atmosphere containing ahalogen compound, or the plant-derived char can be mixed and calcinedwith the volatile organic substance, so as to adjust the nitrogenelement content to the range.

An oxygen element content contained in the carbonaceous materialobtained in this embodiment is preferably as small as possible andusually has an analysis value obtained from elemental analysis ofpreferably 2.5 mass % or less, more preferably 2.3 mass % or less,further preferably 2 mass % or less, particularly preferably LS mass %or less, extremely preferably 1 mass % or less, especially preferably0.6 mass % or less, most preferably 0.55 mass % or less. It is furtherpreferable that the oxygen element is not substantially contained. Asused herein, “not substantially contained” means that the content isequal to or less than 10⁻⁶ mass %, which is the detection limit of theelemental analysis method (inert gas fusion-thermal conductimetry)described later. If the oxygen element content is excessively large,lithium ions and oxygen react with each other and lithium ions areconsumed, thereby reducing the utilization efficiency of lithium ions.Furthermore, the excessively large oxygen element content not onlyattracts oxygen and moisture in the air to increase a probability ofreaction with the carbonaceous material but also prevents easydesorption when water is adsorbed, resulting in a reduction in theutilization efficiency of lithium ions in some cases. The carbonaceousmaterial obtained by the production method of the present invention alsopreferably has the oxygen element content in the range.

A method of adjusting the oxygen element content to the range is notlimited at all and, for example, the plant-derived char can be subjectedto gas-phase demineralization by a method comprising a step of heattreatment at 500° C. to 940° C. in an inert gas atmosphere containing ahalogen compound, or the plant-derived char can be mixed and calcinedwith the volatile organic substance, so as to adjust the oxygen elementcontent to the range.

From the viewpoints of increasing the dedoping capacity and decreasingthe non-dedoping capacity, the potassium element content contained inthe carbon precursor obtained in this embodiment is preferably 0.1 mass% or less, more preferably 0.05 mass % or less, further preferably 0.03mass % or less, particularly preferably 0.01 mass % or less, especiallypreferably 0.005 mass % or less. From the viewpoints of increasing thededoping capacity and decreasing the non-dedoping capacity, the ironelement content contained in the carbonaceous material obtained in thisembodiment is preferably 0.02 mass % or less, more preferably 0.015 mass% or less, further preferably 0.01 mass % or less, particularlypreferably 0.006 mass % or less, especially preferably 0.004 mass % orless. The content is particularly preferably 0.005 mass % or less andespecially preferably 0.003 mass % or less. When the contents of thepotassium element and/or the iron element contained in the carbonaceousmaterial are not more than the upper limit values described above, thededoping capacity increases, and the dedoping capacity tends todecrease, in a non-aqueous electrolyte secondary battery using thecarbonaceous material. Furthermore, when the contents of the potassiumelement and/or the iron element contained in the carbonaceous materialare not more than the upper limit values described above, a shortcircuit is restrained from occurring due to reprecipitation of thesemetal elements eluted into the electrolytic solution, so that the safetyof the non-aqueous electrolyte secondary battery can be ensured. It isparticularly preferable that the carbonaceous material does notsubstantially contain the potassium element or the iron element.Measurement of the contents of the potassium element and the ironelement can be performed as described above. The potassium elementcontent and the iron element content contained in the carbonaceousmaterial are usually 0 mass % or more. The potassium element content andthe iron element content contained in the carbonaceous material tend tobecome lower when the potassium element content and the iron elementcontent contained in the carbon precursor are smaller. The carbonaceousmaterial obtained by the production method of the present invention alsopreferably has the potassium element content and/or the iron elementcontent in the range.

In the carbonaceous material of the present invention, from theviewpoint of increasing the capacity per mass of the battery, a truedensity ρ_(Bt) according to the butanol method is preferably 1.4 to 1.7g/cm³, more preferably 1.42 to 1.65 g/cm³, further preferably 1.44 to1.6 g/cm³. The plant-derived char carbon precursor having such a truedensity ρ_(Bt) can be produced by calcining a plant raw material at 800to 1400° C., for example. Details of the measurement of the true densityρ_(Bt) are as described in Examples, and the true density ρ_(Bt) can bemeasured by the butanol method according to the method defined in JIS R7212. The carbonaceous material obtained by the production method of thepresent invention also preferably has the true density ρ_(Bt) in therange.

The carbonaceous material of the present invention preferably has Lc (ina hexagonal carbon layer stack direction) of 3 nm or less from theviewpoint of repetitive characteristics in doping and dedoping oflithium particularly required for automotive applications etc. Lc ismore preferably 0.5 to 2 nm. When Lc exceeds 3 nm, the carbon hexagonallayers are stacked in multiple layers, and the volumeexpansion/shrinkage accompanying doping/dedoping of lithium mayincrease. Therefore, the carbon structure is destroyed due to the volumeexpansion/shrinkage, and the doping/dedoping of lithium is blocked, sothat the repetitive characteristics may deteriorate. Details of themeasurement of Lc are as described in Examples and Lc can be obtained byusing the Scherrer's equation according to the X-ray diffraction method.The carbonaceous material obtained by the production method of thepresent invention also preferably has Lc within the range.

The average particle diameter (D50) of the carbonaceous material of thepresent invention is 1 to 4 μm. If the average particle diameter isexcessively small, fine powder increases and the specific surface areaof the carbonaceous material increases. Consequently, the reactivitybetween the carbonaceous material and the electrolytic solution becomeshigher, and the irreversible capacity increases, so that a proportion ofwasted capacity may increase in the positive electrode. The irreversiblecapacity is a capacity not to be discharged out of the charged capacityof the non-aqueous electrolyte secondary battery. When a negativeelectrode (electrode) is produced by using a carbonaceous materialhaving an excessively small average particle diameter, smaller gaps areformed in the carbonaceous material, so that migration of lithium in theelectrolytic solution is restricted, which is not preferable. Theaverage particle diameter of the carbonaceous material is 1 μm or more,preferably 1.2 μm or more, for example, 1.5 μm or more. When the averageparticle diameter is 4 μm or less, a small diffusion free path oflithium in the particles enables rapid charging and discharging.Furthermore, in lithium ion secondary batteries, it is important toincrease an electrode area for improvement of input/outputcharacteristics, and therefore, a coating thickness of an activematerial applied to a collector plate needs to be reduced at the time ofelectrode fabrication. To reduce the coating thickness, it is necessaryto reduce the particle diameter of the active material. From such aviewpoint, the upper limit of the average particle diameter is 4 μm orless, preferably 3.5 μm or less, more preferably 3.2 μm or less, furtherpreferably 3 μm or less, particularly preferably 2.8 μm or less. Thecarbonaceous material obtained by the production method of the presentinvention also preferably has the average particle diameter (D50) in therange.

An amount of moisture absorption of the carbonaceous material of thepresent invention is preferably 50,000 ppm or less, more preferably45,000 ppm or less, further preferably 40,000 ppm or less, furthermorepreferably 15,000 ppm or less, especially preferably 14,000 ppm or less,most preferably 8,000 ppm or less. A smaller amount of moistureabsorption reduces the moisture adsorbed on the carbonaceous material,increases the lithium ions adsorbed on the carbonaceous material, and istherefore preferable. Additionally, a smaller amount of moistureabsorption can reduce the reaction between the adsorbed moisture and thenitrogen atoms of the carbonaceous material and the self-discharge dueto the reaction between the adsorbed moisture and lithium ions and istherefore preferable. The amount of moisture absorption of thecarbonaceous material can be decreased by reducing the amounts ofnitrogen atoms and oxygen atoms contained in the carbonaceous material,for example. The amount of moisture absorption of the carbonaceousmaterial can be measured by using Karl Fischer, for example. Thecarbonaceous material obtained by the production method of the presentinvention also preferably has the amount of moisture absorption in therange.

(Negative Electrode for Non-Aqueous Electrolyte Secondary Battery)

A negative electrode for a non-aqueous electrolyte secondary battery ofthe present invention comprises the carbonaceous material for anon-aqueous electrolyte secondary battery of the present invention. Thecarbonaceous material obtained by the production method of the presentinvention can be used as the carbonaceous material for a non-aqueouselectrolyte secondary battery of the present invention, for example, thenegative electrode (electrode) for a non-aqueous electrolyte secondarybattery.

A method for producing a negative electrode for a non-aqueouselectrolyte secondary battery of the present invention will hereinafterspecifically be described. The negative electrode (electrode) of thepresent invention can be produced by adding a binder to the carbonaceousmaterial of the present invention, adding an appropriate amount of asuitable solvent, kneading the material into an electrode mixture, andthen applying and drying the mixture on a collector plate made up of ametal plate etc., before performing pressure forming.

By using the carbonaceous material of the present invention, ahighly-conductive electrode can be produced without adding a conductiveassistant. For the purpose of imparting higher conductivity, aconductive assistant can be added at the time of preparation of theelectrode mixture as needed. Conductive carbon black, vapor-grown carbonfibers (VGCF), nanotube, etc. can be used as the conductive assistant.Although an addition amount of the conductive assistant varies dependingon a kind of the conductive assistant to be used, the expectedconductivity may not be obtained if the addition amount is too small,and the dispersion in the electrode mixture may be poor if the amount istoo large. From such a viewpoint, a preferable proportion of theconductive assistant to be added is 0.5 to 10 mass % (assuming theamount of the active material (carbonaceous material)+the amount of thebinder+the amount of the conductive assistant=100 mass %), morepreferably 0.5 to 7 mass %, particularly preferably 0.5 to 5 mass %. Thebinder may be any binder not reactive with an electrolytic solution,such as PVDF (polyvinylidene fluoride), polytetrafluoroethylene, and amixture of SBR (styrene-butadiene rubber) and CMC (carboxymethylcellulose), without particular limitation. Among others, PVDF ispreferable since PVDF having adhered to the surface of the activematerial is less likely to inhibit the lithium ion migration so thatfavorable input/output characteristics are easily obtained. Although apolar solvent such as N-methylpyrrolidone (NMP) is preferably used fordissolving the PVDF and forming a slurry, an aqueous emulsion such asSBR or CMC dissolved in water can also be used. If the addition amountof the binder is too large, the resistance of the obtained electrodebecomes large, so that an increased internal resistance of the batterymay deteriorate the battery performance. On the other hand, if theaddition amount of the binder is too small, bonding between theparticles of the negative electrode material and with the collectorplate may be insufficient. Although a preferable addition amount of thebinder varies depending on a kind of the binder to be used, for example,the addition amount of the PVDF-based binder preferably is 3 to 13 mass%, more preferably 3 to 10 mass %. On the other hand, when water is usedas a solvent of the binder, a plurality of binders is often mixed andused as in the case of a mixture of SBR and CMC, and the total amount ofall the binders to be used is preferably 0.5 to 5 mass %, morepreferably 1 to 4 mass %.

An electrode active material layer is basically formed on both sides ofthe collector plate or may be formed on one side as necessary. Thethicker electrode active material layer is preferable for highercapacity since the collector plate, a separator, etc. can be reduced.However, a wider electrode area opposed to a counter electrode is moreadvantageous for improvement of the input/output characteristics, andtherefore, when the electrode active material layer is too thick, theinput/output characteristics may deteriorate. From the viewpoint ofoutput during battery discharge, a preferable thickness of the activematerial layer (per one side) is preferably 10 to 80 μm, more preferably20 to 75 μm, further preferably 20 to 60 μm.

(Non-Aqueous Electrolyte Secondary Battery)

A non-aqueous electrolyte secondary battery of the present inventioncomprises the negative electrode for a non-aqueous electrolyte secondarybattery of the present invention. By using the negative electrode for anon-aqueous electrolyte secondary battery produced by the productionmethod of the present invention, the non-aqueous electrolyte secondarybattery can be provided. The non-aqueous electrolyte secondary batteryof the present invention has favorable discharge capacity and favorableresistance to oxidative deterioration. The non-aqueous electrolytesecondary battery of the present invention has favorable resistance tooxidative deterioration, suppresses an increase in irreversible capacitydue to inactivation of lithium ions, and can maintain highcharge/discharge efficiency. A non-aqueous electrolyte secondary batteryusing the negative electrode for a non-aqueous electrolyte secondarybattery using the carbonaceous material of the present invention or thecarbonaceous material obtained by the production method of the presentinvention exhibits excellent output characteristics and excellent cyclecharacteristics.

If the negative electrode for a non-aqueous electrolyte secondarybattery is formed by using the carbonaceous material of the presentinvention or the carbonaceous material obtained by the production methodof the present invention, various materials conventionally used orproposed for non-aqueous electrolyte secondary batteries can be used forother materials constituting the battery, such as a positive electrodematerial, the separator, and the electrolytic solution, withoutparticular limitation.

For example, for the positive electrode material, layered oxide-based(represented by LiMO₂, where M is metal: e.g., LiCoO₂, LiNiO₂, LiMnO₂,or LiNi_(x)Co_(y)Mo_(z)O₂ (x, y, and z represent composition ratios)),olivine-based (represented by LiMPO₄, where M is metal: e.g., LiFePO₄),and spinel-based (represented by LiM₂O₄, where M is metal: e.g.,LiMn₂O₄) composite metal chalcogen compounds are preferable, and thesechalcogen compounds may be mixed as needed. The positive electrode isformed by shaping these positive electrode materials together with asuitable binder and a carbon material for imparting conductivity to anelectrode such that a layer is formed on the conductive collector plate.

A non-aqueous solvent type electrolyte solution used in combination withthese positive and negative electrodes is generally formed by dissolvingan electrolyte in a non-aqueous solvent. For the non-aqueous solvent,for example, one or more organic solvents such as propylene carbonate,ethylene carbonate, dimethyl carbonate, diethyl carbonate,dimethoxyethane, diethoxyethane, γ-butyrolactone, tetrahydrofuran,2-methyltetrahydrofuran, sulfolane, or 1,3-dioxolane can be used aloneor in combination. For the electrolyte, LiClO₄, LiPF₆, LiBF₄, LiCF₃SO₃,LiAsF₆, LiCl, LiBr, LiB(C₆H₅)₄, or LiN(SO₃CF₃)₂ is used.

The non-aqueous electrolyte secondary battery is generally formed byimmersing in the electrolytic solution the positive electrode and thenegative electrode formed as described above and opposed to each otheracross a liquid-permeable separator made of nonwoven fabric or otherporous materials as needed. For the separator, a permeable separatormade of nonwoven fabric normally used for a secondary battery or otherporous materials can be used. Alternatively, a solid electrolyte made ofpolymer gel impregnated with an electrolytic solution may be usedinstead of, or together with, the separator.

The carbonaceous material for a non-aqueous electrolyte secondarybattery of the present invention or the carbonaceous material for anon-aqueous electrolyte secondary battery obtained by the productionmethod of the present invention is suitable for a carbonaceous materialfor a battery (typically, a non-aqueous electrolyte secondary batteryfor driving a vehicle) mounted on a vehicle such as an automobile. Inthe present invention, the vehicle refers to a vehicle generally knownas an electric vehicle, a hybrid vehicle with a fuel cell and aninternal combustion engine, etc. without particular limitation; however,the vehicle at least comprises a power source device provided with thebattery, an electric drive mechanism driven by power supply from thepower source device, and a control device controlling this mechanism.The vehicle may further comprise a mechanism provided with a powergeneration brake and a regenerative brake and converting energy frombraking into electricity to charge the non-aqueous electrolyte secondarybattery.

EXAMPLES

The present invention will hereinafter specifically be described withexamples; however, the present invention is not limited to theseexamples. A method for measuring physical property values of thecarbonaceous material for a non-aqueous electrolyte secondary batterywill hereinafter be described; however, the physical property valuesdescribed in this description comprising the examples are based onvalues obtained by the following method.

(Measurement of Specific Surface Area by Nitrogen Adsorption BETThree-Point Method)

An approximate expression (Eq. (II)) derived from the BET equation isdescribed below.[Mathematical 2]p/[v(p ₀ −p)]=(1/v _(m) c)+[(c−1)/v _(m) c](p/p ₀)  (II)

By using the approximate expression, v_(m) was obtained by a three-pointmethod according to nitrogen adsorption at liquid nitrogen temperature,and a specific surface area of a sample was calculated by following Eq.(III).

$\begin{matrix}\left\lbrack {{Mathematical}\mspace{14mu} 3} \right\rbrack & \; \\{{{specific}\mspace{14mu}{surface}\mspace{14mu}{area}} = {\left( \frac{v_{m}{Na}}{22400} \right) \times 10^{- 18}}} & ({III})\end{matrix}$

In the examples, v_(m) is the adsorption amount (cm³/g) required forforming a monomolecular layer on a sample surface, v is the actuallymeasured adsorption amount (cm³/g), p₀ is the saturated vapor pressure,p is the absolute pressure, c is the constant (reflecting the adsorptionheat), N is the Avogadro's number 6.022×10²³, and a (nm²) is the areaoccupied by adsorbate molecules on the sample surface (molecularoccupied cross-sectional area).

Specifically, the adsorption amount of nitrogen to the sample at liquidnitrogen temperature was measured by using “BELL Sorb Mini” manufacturedby BEL Japan as follows. After the sample was filled in a sample tube,the sample tube cooled to −196° C. was once depressurized beforenitrogen (purity 99.999%) was adsorbed to the sample at a desiredrelative pressure. An adsorbed gas amount v was defined as an amount ofnitrogen adsorbed to the sample when the equilibrium pressure wasreached at each desired relative pressure.

(Measurement of Average Interplanar Spacing d₀₀₂ Using Bragg EquationAccording to Wide-Angle X-Ray Diffraction Method)

By using “MiniFlex II manufactured by Rigaku Corporation”, carbonaceousmaterial powder was filled in a sample holder and the CuKα raymonochromatized by an Ni filter was used as a radiation source to obtainan X-ray diffraction pattern. A peak position of the diffraction patternwas obtained by a gravity center method (a method of obtaining a gravitycenter position of a diffraction line to obtain a peak position with a2θ value corresponding thereto) and was corrected by using a diffractionpeak of the (111) plane of high purity silicon powder for standardmaterial. A wavelength λ of the CuKα ray was set to 0.15418 nm, and d₀₀₂was calculated according to the Bragg formula (Eq. (IV)) describedbelow.

$\begin{matrix}\left\lbrack {{Mathematical}\mspace{14mu} 4} \right\rbrack & \; \\{d_{002} = {\frac{\lambda}{{2 \cdot \sin}\mspace{11mu}\theta}\left( {{Bragg}\mspace{14mu}{formula}} \right)}} & ({IV})\end{matrix}$(Elemental Analysis)

Elemental analysis was performed by using the oxygen/nitrogen/hydrogenanalyzer EMGA-930 manufactured by HORIBA, Ltd.

The detection methods of the apparatus are oxygen: inert gasfusion-non-dispersive infrared absorption method (NDIR), nitrogen: inertgas fusion-thermal conductivity method (TCD), and hydrogen: inert gasfusion-non-dispersive infrared absorption method (NDIR) calibrated withan (oxygen/nitrogen) Ni capsule, TiH₂ (H standard sample), and SS-3 (N,O standard sample), and 20 mg of a sample having moisture contentmeasured at 250° C. for about 10 minutes for a pretreatment was put intoan Ni capsule and measured after 30 seconds of degasification in theanalyzer. The test was performed by analyzing three specimens, and anaverage value was used as an analysis value.

(Measurement of Residual Carbon Ratio)

The residual carbon ratio was measured by quantifying a carbon contentof an ignition residue after ignition of a sample in an inert gas. Withregard to the ignition, about 1 g of a volatile organic substance (theaccurate mass is defined as W₁ (g)) was put into a crucible and thecrucible was heated in an electric furnace at the temperature increaserate of 10° C./min from ordinary temperature to 800° C. while flowing 20liters of nitrogen per minute and was then ignited at 800° C. for 1hour. A residue in this case was defined as the ignition residue, andthe mass thereof was defined as W₂ (g).

Subsequently, for the ignition residue, elemental analysis was performedin accordance with the method defined in JIS M 8819 to measure a massproportion P₁ (%) of carbon. A residual carbon ratio P₂ (mass %) wascalculated by Eq. 1 described above.

(Measurement of True Density by Butanol Method)

The true density ρ_(Bt) was measured by the butanol method according tothe method defined in JIS R 7212. A mass (m₁) of a pycnometer with aside tube having an inner volume of about 40 mL was accurately measured.Subsequently, a sample was placed flatly on a bottom portion thereof toa thickness of about 10 mm, and a mass (m₂) thereof was accuratelymeasured. To this sample, 1-Butanol was gently added such that the depthfrom the bottom was about 20 mm. Subsequently, after applying mildvibrations to the pycnometer and confirming that large bubbles were nolonger generated, the pycnometer was placed in a vacuum desiccator andgradual evacuation was performed to 2.0 to 2.7 kPa. After the pressurewas kept for 20 minutes or more and the generation of bubbles wasstopped, the pycnometer was removed, filled with 1-butanol, plugged, andplaced in a constant temperature water bath (adjusted to 30±0.03° C.)for 15 minutes or more with the liquid surface of 1-butanol beingaligned with a marked line. After the pycnometer was taken out and theexterior portion thereof was sufficiently wiped, cooling to ordinarytemperature was followed by accurate measurement of a mass (m₄).Subsequently, the same pycnometer was filled only with 1-butanol andplaced in the constant temperature water bath as described above, and amass (m₃) was measured after alignment with the marked line. Distilledwater with dissolved gas being removed by boiling immediately before usewas taken in the pycnometer, which was then placed in the constanttemperature water bath as described above, and a mass (m₅) was measuredafter alignment with the marked line. The true density ρ_(Bt) wascalculated by following Eq. (V). In this equation, d is the specificgravity (0.9946) of water at 30° C.

$\begin{matrix}\left\lbrack {{Mathematical}\mspace{14mu} 5} \right\rbrack & \; \\{\rho_{Bt} = {\frac{m_{2} - m_{1}}{m_{2} - m_{1} - \left( {m_{4} - m_{3}} \right)} \times \frac{m_{3} - m_{1}}{m_{5} - m_{1}}d}} & (V)\end{matrix}$(Measurement of Average Particle Diameter by Laser Scattering Method)

The average particle diameter (particle size distribution) of theplant-derived char and the carbonaceous material was measured by thefollowing method. The sample was put into an aqueous solution containing0.3 mass % surfactant (“Toriton X100” manufactured by Wako Pure ChemicalIndustries), treated by an ultrasonic cleaner for 10 minutes or more,and dispersed in the aqueous solution. The particle size distributionwas measured by using this dispersion. Particle size distributionmeasurement was performed by using a particle diameter/particle sizedistribution measuring device (“Microtrac MT3000” manufactured byNikkiso). D50 is the particle diameter at which the cumulative volume is50%, and this value was used as the average particle diameter.

(Metal Content Measurement)

With regard to a method for measuring potassium element content and ironelement content, the following method was used for the measurement. Acarbon sample containing predetermined potassium element and ironelement was prepared in advance to create calibration curves for arelation between the potassium Kα ray intensity and the potassiumelement content and a relation between the iron Kα ray intensity and theiron element content, using fluorescent X-ray analyzer. Then, theintensities of the potassium Kα ray and the iron Kα ray in fluorescentX-ray analysis of the sample were measured to obtain the potassiumelement content and the iron element content from the calibration curvescreated in advance. The fluorescent X-ray analysis was performed underthe following conditions by using LAB CENTER XRF-1700 manufactured byShimadzu Corporation. A holder for an upper irradiation method was usedand a sample measurement area was set within a circumference of 20 mm indiameter. For setting a sample to be measured, 0.5 g of the sample to bemeasured was placed in a polyethylene container having an inner diameterof 25 mm with the back being pressed by a plankton net, and ameasurement surface was covered with polypropylene film when measurementwas performed. The X-ray source was set to 40 kV and 60 mA. Potassiumwas measured by using LiF (200) as a dispersive crystal and a gas flowtype proportional counter tube as a detector in the range of 2θ of 90°to 140° at a scanning speed of 8°/min. Iron was measured by using LiF(200) as a dispersive crystal and a scintillation counter as a detectorin the range of 2θ of 56° to 60° at a scanning speed of 8°/min.

(Measurement of Amount of Moisture Absorption)

Ten grams of the sample was put into a sample tube and preliminarilydried at 120° C. for two hours under the reduced pressure of 133 Pa andwas transferred to a glass petri dish of 50 mm in diameter and exposedin a constant temperature and humidity chamber at 25° C. and thehumidity of 50% for a predetermined time. Subsequently, 1 g of thesample was weighed and taken and then heated to 250° C. in Karl Fischer(manufactured by Mitsubishi Chemical Analytech) to measure an amount ofmoisture absorption under a nitrogen gas stream.

Preparation Example 1

Coconut shell was crushed and dry distilled at 500° C. to obtain acoconut shell char having a particle diameter of 2.360 to 0.850 mm(containing 98 mass % of particles having a particle diameter of 2.360to 0.850 mm). A gas-phase demineralization treatment was performed for100 g of this coconut shell char at 900° C. for 50 minutes whilesupplying a nitrogen gas containing 1 vol % hydrogen chloride gas at aflow rate of 10 L/min. Subsequently, only the supply of the hydrogenchloride gas was stopped, and a gas-phase deacidification treatment wasfurther performed at 900° C. for 30 minutes while supplying the nitrogengas at a flow rate of 10 L/min to obtain a carbon precursor.

The obtained carbon precursor was pulverized by using a dry bead mill(ball mill) (SDAS manufactured by Ashizawa Finetech) under conditions ofa bead diameter of 3 mm, a bead filling rate of 75%, and a raw materialfeed amount of 1 kg/Hr to obtain a carbon precursor (1) having anaverage particle diameter of 2.5 μm and a specific surface area of 467m²/g.

Preparation Example 2

A carbon precursor (2) having an average particle diameter of 1.8 μm anda specific surface area of 484 m²/g was obtained as in PreparationExample 1 except that the raw material feed amount was changed to 0.5kg/Hr.

Preparation Example 3

A carbon precursor (3) having an average particle diameter of 4.2 μm anda specific surface area of 401 m²/g was obtained as in PreparationExample 1 except that the raw material feed amount was changed to 1.3kg/Hr.

Preparation Example 4

A carbon precursor (4) having an average particle diameter of 0.7 μm anda specific surface area of 581 m²/g was obtained as in PreparationExample 1 except that the raw material feed amount was changed to 0.2kg/Hr.

Preparation Example 5

A carbon precursor (5) having an average particle diameter of 5.5 μm anda specific surface area of 392 m²/g was obtained as in PreparationExample 1 except that the raw material feed amount was changed to 1.63kg/Hr.

Example 1

In a high-speed temperature rising furnace manufactured by Motoyama, 10g of the carbon precursor (1) prepared in Preparation Example 1 andplaced in a graphite setter (a graphite sheath) (100 mm in length, 100mm in width, 50 mm in height) was elevated in temperature to 1290° C.(calcining temperature) at a heat rising rate of 60° C. per minute undera nitrogen flow rate of 5 L per minute and was then held for 23 minutesbefore natural cooling. After confirming that the furnace temperaturehad decreased to 100° C. or less, a carbonaceous material (1) was takenout from the furnace. The mass of the recovered carbonaceous material(1) was 9.1 g, and the recovery rate to the carbon precursor (1) was91%. Physical properties of the obtained carbonaceous material (1) areshown in Table 1.

Example 2

A carbonaceous material (2) was obtained as in Example 1 except that thecarbon precursor (2) prepared in Preparation Example 2 was used insteadof the carbon precursor (1). The recovery amount was 9.1 g, and therecovery rate was 91%. Physical properties of the obtained carbonaceousmaterial (2) are shown in Table 1.

Example 3

With 9.1 g of the carbon precursor (5) prepared in Preparation Example5, 0.9 g of polystyrene (manufactured by Sekisui Plastics and having anaverage particle diameter of 400 μm and a residual carbon ratio of 1.2mass %) was mixed. In a high-speed temperature rising furnacemanufactured by Motoyama, 10 g of this mixture placed in a graphitesetter (100 mm in length, 100 mm in width, 50 mm in height) was elevatedin temperature to 1290° C. at a heat rising rate of 60° C. per minuteunder a nitrogen flow rate of 5 L per minute and was then held for 23minutes before natural cooling. After confirming that the furnacetemperature had decreased to 100° C. or less, a carbonaceous materialwas taken out from the furnace. The mass of the recovered carbonaceousmaterial was 8.1 g, and the recovery rate to the carbon precursor was91%.

The obtained carbonaceous material was placed in an 80 mL zirconiacontainer filled with zirconia beads having a bead diameter of 5 mm andwas pulverized by repeating a step of rotating at 400 rpm for 5 minutesand then stopping for 1 minute 15 times by using a dry ball mill (P-6manufactured by Fritsch) to obtain a carbonaceous material (3) having anaverage particle diameter of 2.9 μm. Physical properties of the obtainedcarbonaceous material (3) are shown in Table 1.

Example 4

In a high-speed temperature rising furnace manufactured by Motoyama, 10g of the carbon precursor (5) prepared in Preparation Example 5 andplaced in a graphite setter (100 mm in length, 100 mm in width, 50 mm inheight) was elevated in temperature to 1290° C. at a heat rising rate of60° C. per minute under a nitrogen flow rate of 5 L per minute and wasthen held for 23 minutes before natural cooling. After confirming thatthe furnace temperature had decreased to 100° C. or less, a carbonaceousmaterial was taken out from the furnace. The mass of the recoveredcarbonaceous material was 9.1 g, and the recovery rate to the carbonprecursor was 91%.

The obtained carbonaceous material was placed in an 80 mL zirconiacontainer filled with zirconia beads having a bead diameter of 5 mm andwas pulverized by repeating a step of rotating at 400 rpm for 5 minutesand then stopping for 1 minute 15 times by using a ball mill (P-6manufactured by Fritsch) to obtain a carbonaceous material (4). Physicalproperties of the obtained carbonaceous material (4) are shown in Table1.

Comparative Example 1

A carbonaceous material (5) was obtained as in Example 1 except that thecalcining temperature was changed to 1370° C. The recovery amount was9.2 g, and the recovery rate was 92%. Physical properties of theobtained carbonaceous material (5) are shown in Table 1.

Comparative Example 2

A carbonaceous material (6) was obtained as in Example 1 except that thecalcining temperature was changed to 1200° C. The recovery amount was9.1 g, and the recovery rate was 91%. Physical properties of theobtained carbonaceous material (6) are shown in Table 1.

Comparative Example 3

A carbonaceous material (7) was obtained as in Example 1 except that thecarbon precursor (5) was used instead of the carbon precursor (1). Therecovery amount was 9.1 g, and the recovery rate was 91%. Physicalproperties of the obtained carbonaceous material (7) are shown in Table1.

Comparative Example 4

A carbonaceous material (8) was obtained as in Example 1 except that thecarbon precursor (6) was used instead of the carbon precursor (1). Therecovery amount was 9.2 g, and the recovery rate was 92%. Physicalproperties of the obtained carbonaceous material (8) are shown in Table1.

Comparative Example 5

A carbonaceous material (9) was obtained as in Example 3 except that thecarbon precursor (5) prepared in Preparation Example 5 was notpulverized after firing. Physical properties of the obtainedcarbonaceous material (9) are shown in Table 1.

Comparative Example 6

A carbonaceous material (10) was obtained as in Example 3 except thatthe number of repetitions of the process of rotating for 5 minutes andthen stopping for 1 minute in the dry ball mill was changed to 20 times.Physical properties of the obtained carbonaceous material (10) are shownin Table 1.

Comparative Example 7

A carbonaceous material (11) was obtained as in Example 4 except thatthe carbon precursor (5) prepared in Preparation Example 5 was notpulverized after firing. Physical properties of the obtainedcarbonaceous material (11) are shown in Table 1.

TABLE 1 specific average nitrogen oxygen amount of K Fe surface particleelement element true moisture element element d₀₀₂ area diameter contentcontent density absorption content content (nm) (m²/g) (μm) (mass %)(mass %) (g/cm³) (ppm) (ppm) (ppm) Examples 1 0.389 42 2.5 0.14 0.451.50 32448 27 16 2 0.388 45 1.8 0.13 0.51 1.50 35559 35 19 3 0.389 272.9 0.17 1.99 1.50 27445 32 17 4 0.386 45 2.9 0.17 1.79 1.50 31146 27 18Comparative 1 0.389 17 2.5 0.15 0.45 1.49 30812 35 20 Examples 2 0.38966 2.5 0.14 0.78 1.49 35316 36 18 3 0.389 42 4.2 0.15 0.59 1.46 29566 3617 4 0.389 42 0.7 0.15 1.77 1.49 44112 35 17 5 0.389 5 5.5 0.14 0.471.47 4913 32 17 6 0.389 80 0.9 0.14 2.55 1.51 51222 31 18 7 0.389 7 5.50.14 0.59 1.47 5412 32 18(Fabrication of Electrode)

By using the carbonaceous materials (1) to (11) obtained in Examples 1and 4 and Comparative Examples 1 to 7, respective electrodes (negativeelectrodes) were fabricated according to the following procedure.

A slurry was obtained by mixing 92 parts by mass of the preparedcarbonaceous material, 2 parts by mass of acetylene black, 6 parts bymass of PVDF (polyvinylidene fluoride), and 90 parts by mass of NMP(N-methylpyrrolidone). The obtained slurry was applied to a copper foilhaving a thickness of 14 μm, dried, and then pressed to obtainrespective electrodes (1) to (11) having a thickness of 60 μm. Theobtained electrodes (1) to (11) had a density of 0.9 to 1.1 g/cm³.

(Measurement of Charge Capacity, Discharge Capacity, Charge/DischargeEfficiency, and Initial DC Resistance)

The electrodes (1) to (11) fabricated as described above were used asworking electrodes while metal lithium was used as counter electrodesand reference electrodes. For a solvent, a mixture of ethylene carbonateand methylethyl carbonate (volume ratio 3:7) were used. In this solvent,1 mol/L of LiPF₆ was dissolved and used as an electrolyte. A glass fibernonwoven fabric was used for the separator. Respective coin cells werefabricated in a glove box under an argon atmosphere.

For the lithium ion secondary batteries having the structure describedabove, a charge/discharge test was performed by using a charge/dischargetest apparatus (“TOSCAT” manufactured by Toyo System). The initial DCresistance was defined as a resistance value generated when 0.5 mA wasapplied for 3 seconds. Doping of lithium was performed at a rate of 70mA/g with respect to the active material mass, and doping was performedto 1 mV with respect to lithium potential. A constant voltage of 1 mVrelative to the lithium potential was further applied for 8 hours beforeterminating the doping. A capacity (mAh/g) at this point was defined asthe charge capacity. Subsequently, dedoping was performed at a rate of70 mA/g with respect to the active material mass to 2.5 V relative tothe lithium potential, and a capacity discharged at this point wasdefined as the discharge capacity. The percentage of the dischargecapacity/charge capacity was defined as the charge/discharge efficiency(charge/discharge efficiency) and was used as an index of theutilization efficiency of lithium ions in the battery. The obtainedbattery performance is shown in Table 2.

TABLE 2 charge discharge charge/ initial DC capacity capacity dischargeresistance (mAh/g) (mAh/g) efficiency (%) (Ω) Examples 1 443 340 77 3772 442 344 78 357 3 441 352 80 343 4 436 340 76 316 Comparative 1 421 33780 402 Examples 2 466 349 75 501 3 443 345 78 612 4 451 324 72 551 5 386336 87 899 6 458 321 70 250 7 391 325 83 812

From Table 2, in the results from the lithium ion secondary batteriesfabricated by using the carbonaceous materials obtained in Examples 1 to4, a high charge capacity and a high discharge capacity were obtained atthe same time, and furthermore, the charge/discharge efficiency wasexcellent. In Examples 1 to 4, the initial DC resistance was low. As aresult, it is clear that the non-aqueous electrolyte secondary batteryusing the negative electrode containing the carbonaceous material of thepresent invention exhibits favorable charge/discharge capacities as wellas low resistance.

The invention claimed is:
 1. A carbonaceous material for a non-aqueouselectrolyte secondary battery, having an average interplanar spacingd₀₀₂ of the (002) plane of from 0.36 to 0.42 nm calculated by using theBragg equation according to a wide-angle X-ray diffraction method, aspecific surface area of from 20 to 65 m²/g obtained by a nitrogenadsorption BET three-point method, a nitrogen element content of 0.3mass % or less, an oxygen element content of 2.5 mass % or less, and anaverage particle diameter of from 1 to 4 μm according to a laserscattering method, and a true density of from 1.4 to 1.7 g/cm³ obtainedby a butanol method.
 2. The carbonaceous material according to claim 1,wherein the carbonaceous material has a potassium element content of 0.1mass % or less and an iron element content of 0.02 mass % or less.
 3. Anegative electrode for a non-aqueous electrolyte secondary battery,comprising the carbonaceous material according to claim
 1. 4. Anon-aqueous electrolyte secondary battery, comprising the negativeelectrode according to claim
 3. 5. A method for producing a carbonaceousmaterial for a non-aqueous electrolyte secondary battery, the methodcomprising: calcining a carbon precursor or a mixture of the carbonprecursor and a volatile organic substance under an inert gas atmosphereat 800 to 1400° C., wherein the carbonaceous material for a non-aqueouselectrolyte secondary battery has an average interplanar spacing d₀₀₂ ofthe (002) plane of from 0.36 to 0.42 nm calculated by using the Braggequation according to a wide-angle X-ray diffraction method, a specificsurface area of from 20 to 65 m²/g obtained by a nitrogen adsorption BETthree-point method, a nitrogen element content of 0.3 mass % or less, anoxygen element content of 2.5 mass % or less, an average particlediameter of from 1 to 4 μm according to a laser scattering method, and atrue density of from 1.4 to 1.7 g/cm³ obtained by a butanol method. 6.The method for producing a carbonaceous material for a non-aqueouselectrolyte secondary battery according to claim 5, comprising: thecalcining step, and a post-pulverization step, a post-classificationstep, or both, of adjusting the specific surface area of thecarbonaceous material obtained by a nitrogen adsorption BET three-pointmethod to 20 to 75 m²/g through pulverization, classification, or both.7. The method according to claim 5, further comprising apre-pulverization step, a pre-classification step, or both, of adjustingthe specific surface area of the carbon precursor obtained by a nitrogenadsorption BET three-point method to 100 to 800 m²/g throughpulverization, classification, or both.
 8. The method according to claim5, wherein the carbon precursor is derived from a plant.
 9. The methodaccording to claim 5, wherein the volatile organic substance is in asolid state at ordinary temperature and has a residual carbon ratio ofless than 5 mass %.
 10. The method according to claim 5, wherein thecarbonaceous material has an average interplanar spacing d₀₀₂ of the(002) plane within a range of 0.36 to 0.42 nm calculated by using theBragg equation according to a wide-angle X-ray diffraction method, anitrogen element content of 0.3 mass % or less, an oxygen elementcontent of 2.5 mass % or less, and an average particle diameter of 1 to4 μm according to a laser scattering method.
 11. The method according toclaim 5, wherein the carbonaceous material has a potassium elementcontent of 0.1 mass % or less and an iron element content of 0.02 mass %or less.